The present invention relates to an exhaust gas recirculation device for recirculating, from an exhaust system to an intake system, a part of exhaust gas discharged from each of a plurality of cylinders which are provided to a multi-cylinder engine as EGR gas.
Conventional exhaust gas recirculation devices of multi-cylinder engines includes an exhaust gas recirculation device disclosed in JP1993-108928A. This device is for an in-line four-cylinder engine having four cylinders aligned in a specific direction. The device includes exhaust gas recirculating passages extending from respective exhaust ports of the cylinders of the engine, an exhaust gas distributing block connected to each exhaust gas recirculating passage on a downstream side and communicated with independent intake passages (four intake passages coupling the intake ports of the cylinders to a surge tank) of the engine, and openable-and-closeable EGR valves (exhaust gas recirculating control valves) provided between the exhaust gas recirculating passage and the exhaust gas distributing block. Exhaust gas led out through the exhaust gas recirculating passage (EGR gas) is further led into the common exhaust gas distributing block, and then further introduced into the respective independent intake passages of the cylinders.
However, as described in JP1993-108928A, with the common exhaust gas distributing block provided between the exhaust gas recirculating passage and the independent intake passages of the cylinders, intake interference occurs between the cylinders through this exhaust gas distributing block, and additionally, it is concerned with the level of the intake interference varying among the cylinders. The variation of intake interference causes a variation in the amount of EGR gas to be led into the cylinders (EGR amount), and a stable combustion may not be performed in all the cylinders.
Obviously, unlike JP1993-108928A, such variation of the EGR amount is reduced by returning the EGR gas, which is led out through the exhaust gas recirculating passages to a large volume surge tank provided upstream of the independent intake passages of the cylinders, and by distributing the exhaust gas from the surge tank to the cylinders. However, in such a case, an opening of the EGR valve is controlled to adjust the EGR amount, followability of the EGR amount to the opening control of the EGR valve degrades, and an unavoidable problem of causing comparatively large response delay arises.